Mary Ainsworth: Strange Situation Experiment & Attachment theory

The strange situation is a standardized procedure devised by Mary Ainsworth in the 1970s to observe attachment security in children within the context of caregiver relationships. It applies to infants between the age of nine and 18 months.

The procedure involves a series of eight episodes lasting approximately 3 minutes each, whereby a mother, child, and stranger are introduced, separated, and reunited.


John Bowlby (1969) believed that attachment was an all-or-nothing process. However, research has shown that there are individual differences in attachment quality. Indeed, one of the primary paradigms in attachment theory is the security of an individual’s attachment (Ainsworth & Bell, 1970).

Much research in psychology has focused on how forms of attachment differ among infants. For example, Schaffer and Emerson (1964) discovered what appeared to be innate differences in sociability in babies; some babies preferred cuddling more than others, from very early on, before much interaction had occurred to cause such differences.

It’s easy to know when you are attached to someone because you know how you feel when you are apart from that person, and, being an adult, you can put your feelings into words and describe how it feels.

However, most attachment research involves infants and young children, so psychologists have to devise subtle ways of researching attachment styles, usually involving the observational method.

Psychologist Mary Ainsworth devised an assessment technique called the Strange Situation Classification (SSC) to investigate how attachments might vary between children.

The Strange Situation was devised by Ainsworth and Wittig (1969) and was based on Ainsworth’s previous Uganda (1967) and later Baltimore studies (Ainsworth et al., 1971, 1978).

Mary Ainsworth’s (1971, 1978) observational study of individual differences in attachment is described below.

Strange Situation Procedure

The security of attachment in one- to two-year-olds was investigated using the strange situation paradigm in order to determine the nature of attachment behaviors and styles of attachment.

Ainsworth and Bell (1971) conducted a controlled observation recording the reactions of a child and mother (caregiver), who were introduced to a strange room with toys. About 100 middle-class American infants and their mothers participated in the strange situation.

The child is observed playing for 20 minutes while caregivers and strangers enter and leave the room, recreating the flow of the familiar and unfamiliar presence in most children’s lives.

Ainsworth & Bell observed from the other side of a one-way mirror, so the children did not know they were being observed.

The infant’s behavior was observed during a set of eight pre-determined  ‘episodes’ of approximately 3 minutes each.

(1) Mother, baby, and experimenter (lasts less than one minute).

(2) Mother and baby alone.

(3) A stranger joins the mother and infant.

(4) Mother leaves baby and stranger alone.

(5) Mother returns and stranger leaves.

(6) Mother leaves; infant left completely alone.

(7) Stranger returns.

(8) Mother returns and stranger leaves.


Observers noted the child’s willingness to explore, separation anxiety, stranger anxiety, and reunion behavior.

Strange Situation classifications (i.e., attachment styles) are based primarily on four interaction behaviors directed toward the mother in the two reunion episodes (Ep. 5 & Ep. 8).

  1. Proximity and contacting seeking
  2. Contact maintaining
  3. Avoidance of proximity and contact
  4. Resistance to contact and comforting

The observers noted the behavior displayed during 15-second intervals and scored the behavior for intensity on a scale of 1 to 7.

strange situation scoring

Behavioral categories allow the researcher to focus on the behaviors to observe clearly. For example, smiling, crying or the baby moving towards or away from the mother.

This allows the observers to tally observations into pre-arranged groupings. It also makes the observations replicable so the results have greater reliability.

Other behaviors observed included:

  • Exploratory behaviors
    e.g., moving around the room, playing with toys, looking around the room.
  • Search behaviors,
    e.g., following mother to the door, banging on the door, orienting to the door, looking at the door, going to mother’s empty chair, looking at mother’s empty chair.
  • Affect Displays negative, e.g., crying, smiling.


Ainsworth (1970) identified three main attachment styles, secure (type B), insecure avoidant (type A), and insecure ambivalent/resistant (type C). She concluded that these attachment styles resulted from early interactions with the mother.

A fourth attachment style, known as disorganized, was later identified (Main, & Solomon, 1990).

Secure Resistant Avoidant
Separation Anxiety Distressed when mother leaves Intense distress when the mother leaves No sign of distress when the the mother leaves
Stranger Anxiety Avoidant of stranger when alone, but friendly when the mother is present The infant avoids the stranger – shows fear of the stranger The infant is okay with the stranger and plays normally when the stranger is present
Reunion behavior Positive and happy when mother returns The infant approaches the mother, but resists contact, may even push her away The Infant shows little interest when the mother returns
Other Uses the mother as a safe base to explore their environment The infant cries more and explores less than the other two types The mother and stranger are able to comfort the infant equally well
% of infants 70% 15% 15%

B: Secure Attachment

Securely attached children comprised most of the sample in Ainsworth’s (1971, 1978) studies.

Infants with this type of attachment explore their environment (explorative behavior) and are moderately distressed when their mother leaves the room (separation anxiety).

They also show moderate stranger anxiety and some distress when they are approached by a stranger. They seek contact with their mother when she returns.

Such children feel confident that the attachment figure will be available to meet their needs. They use the attachment figure as a safe base to explore the environment and seek the attachment figure in times of distress (Main, & Cassidy, 1988).

Securely attached infants are easily soothed by the attachment figure when upset. Infants develop a secure attachment when the caregiver is sensitive to their signals, and responds appropriately to their needs.

According to Bowlby (1980), an individual who has experienced a secure attachment “is likely to possess a representational model of attachment figures(s) as being available, responsive, and helpful” (Bowlby, 1980, p. 242).

A: Insecure Avoidant

Infants with an insecure-avoidant attachment are unconcerned by their mother’s absence when she leaves the room (no separation anxiety).

They show little interest when reunited with the mother (i.e., she returns to the room). Infants are strongly avoidant of the mother and stranger, showing no motivation to interact with either adult. They do not seek contact with the attachment figure when distressed. The stranger is treated similarly to the mother (does not seek contact).

They are very independent of the attachment figure, both physically and emotionally (Behrens, Hesse, & Main, 2007). Insecure avoidant children do not orientate to their attachment figure while investigating the environment.

Such children are likely to have insensitive caregivers who ignore their emotional needs (Ainsworth, 1979).

The attachment figure may withdraw from helping during difficult tasks (Stevenson-Hinde, & Verschueren, 2002) and is often unavailable during emotional distress.

C: Insecure Ambivalent / Resistant

The third attachment style Ainsworth (1970) identified was insecure ambivalent (also called insecure resistant).

Children with this type of attachment are clingy to their mother in a new situation and unwilling to explore. They are extremely distressed when left alone by their mother (separation anxiety), and are scared of the stranger.

When the mother returns, they are pleased to see her and go to her for comfort, but then they cannot be comforted and may show signs of anger towards her.

Here children adopt an ambivalent behavioral style towards the attachment figure. The child commonly exhibits clingy and dependent behavior but rejects the attachment figure when interacting.

The child fails to develop any feelings of security from the attachment figure. Accordingly, they exhibit difficulty moving away from the attachment figure to explore novel surroundings.

When distressed, they are difficult to soothe and are not comforted by interaction with the attachment figure. This behavior results from an inconsistent response to their emotional needs from the primary caregiver.


Ainsworth (1978) suggested the ‘caregiver sensitivity hypothesis’ to explain different attachment types.

Ainsworth’s maternal sensitivity hypothesis argues that a child’s attachment style depends on their mother’s behavior towards them.

  • ‘Sensitive’ mothers are responsive to the child’s needs and respond to their moods and feelings correctly. Sensitive mothers are more likely to have securely attached children.
  • In contrast, mothers who are less sensitive towards their child, for example, those who respond to the child’s needs incorrectly or who are impatient or ignore the child, are likely to have insecurely attached children.

For example, securely attached infants are associated with sensitive and responsive primary care.

Insecure ambivalent attachment is associated with inconsistent primary care. Sometimes the child’s needs and met, and sometimes they are ignored by the caregiver.

Insecure-avoidant attachment is associated with unresponsive primary care. The child comes to believe that communication of needs has no influence on the mother/father.

Ainsworth’s (1971, 1978) findings provided the first empirical evidence for Bowlby’s (1969) theory of internal working models of attachment relationships.

For example, securely attached children develop a positive working model of themselves and have mental representations of others as being helpful while viewing themselves as worthy of respect (Jacobsen, & Hoffman, 1997).

Avoidant children think themselves unworthy and unacceptable, caused by a rejecting primary caregiver (Larose, & Bernier, 2001). Ambivalent children have a negative self-image and exaggerate their emotional responses as a way to gain attention (Kobak et al., 1993).

Accordingly, insecure attachment styles are associated with an increased risk of social and emotional behavioral problems via the internal working model.

attachment styles

Theoretical Evaluation

This caregiver sensitivity theory is supported by research from Wolff and Van Ijzendoorn (1997), who conducted a Meta-analysis (a review) of research into attachment types.

They found that there is a relatively weak correlation of 0.24 between parental sensitivity and attachment type – generally more sensitive parents had securely attached children.

However, in evaluation, critics of this theory argue that the correlation between parental sensitivity and the child’s attachment type is only weak. This suggests that there are other reasons which may better explain why children develop different attachment types and that the maternal sensitivity theory places too much emphasis on the mother.

Focusing just on maternal sensitivity when trying to explain why children have different attachment types is, therefore, a reductionist approach.

An alternative theory proposed by Kagan (1984) suggests that the temperament of the child is actually what leads to the different attachment types. Children with different innate (inborn) temperaments will have different attachment types.

This theory is supported by research from Fox (1989) who found that babies with an ‘Easy’ temperament (those who eat and sleep regularly, and accept new experiences) are likely to develop secure attachments.

Babies with a ‘slow to warm up’ temperament (those who took a while to get used to new experiences) are likely to have insecure-avoidant attachments. Babies with a ‘Difficult’ temperament (those who eat and sleep irregularly and who reject new experiences) are likely to have insecure-ambivalent attachments .

In conclusion, the most complete explanation of why children develop different attachment types would be an interactionist theory. This would argue that a child’s attachment type is a result of a combination of factors – both the child’s innate temperament and their parent’s sensitivity towards their needs.

Belsky and Rovine (1987) propose an interesting interactionist theory to explain the different attachment types. They argue that the child’s attachment type is a result of both the child’s innate temperament and also how the parent responds to them (i.e., the parents’ sensitivity level).

Additionally, the child’s innate temperament may, in fact, influence the way their parent responds to them (i.e, the infants’ temperament influences the parental sensitivity shown to them). To develop a secure attachment, a ‘difficult’ child would need a caregiver who is sensitive and patient for a secure attachment to develop.

Methodological Evaluation

The strange situation classification has been found to have good reliability.  This means that it achieves consistent results.  For example, a study conducted in Germany found 78% of the children were classified in the same way at ages 1 and 6 years (Wartner et al., 1994).

Although, as Melhuish (1993) suggests, the Strange Situation is the most widely used method for assessing infant attachment to a caregiver, Lamb et al. (1985) have criticized it for being highly artificial and lacking ecological validity.

The child is placed in a strange and artificial environment, and the procedure of the mother and stranger entering and leaving the room follows a predetermined script of eight stages (e.g., mum and stranger entering and leaving the room at set times) that would be unlikely to happen in real life.

Mary Ainsworth concluded that the strange situation could be used to identify the child’s type of attachment but has been criticized on the grounds that it identifies only the type of attachment to the mother.

The child may have a different type of attachment to the father or grandmother, for example (Lamb, 1977). This means that it lacks validity, as it does not measure a general attachment style, but instead an attachment style specific to the mother.

In addition, some research has shown that the same child may show different attachment behaviors on different occasions. Children’s attachments may change, perhaps because of changes in the child’s circumstances, so a securely attached child may appear insecurely attached if the mother becomes ill or the family circumstances change.

The strange situation has also been criticized on ethical grounds. Because the child is put under stress (separation and stranger anxiety), the study has broken the ethical guideline protection of participants.

However, in its defense, the separation episodes were curtailed prematurely if the child became too stressed.

Also, according to Marrone (1998), although the Strange Situation has been criticized for being stressful, it simulates everyday experiences, as mothers do leave their babies for brief periods in different settings and often with unfamiliar people such as babysitters.

A problem of the study is that it lacks population validity. The original study used American infants from middle-class families. The study tells us about how this particular group behaves and cannot be generalized to the broader population and other cultures, which might behave differently towards their children and have different expectations.

For example, in Germany, parents encourage independence in their children, so they are less likely to show enthusiastic reunion behavior than children from other cultures.


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Olivia Guy-Evans

BSc (Hons), Psychology, MSc, Psychology of Education

Associate Editor for Simply Psychology

Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.

Saul Mcleod, PhD

Educator, Researcher

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Saul Mcleod, Ph.D., is a qualified psychology teacher with over 18 years experience of working in further and higher education.